1. Field of the Invention
The present invention relates to an imaging apparatus, an imaging system, a method of controlling the apparatus and the system, and a program. More specifically, the present invention relates to a radiation imaging apparatus and a radiation imaging system that can be used in capturing of still and moving images, such as photography, and recording of movies, such as fluoroscopy, in medical diagnosis, a method of controlling the apparatus and the system, and a program.
2. Description of the Related Art
In recent years, radiation imaging apparatuses using flat panel detectors (hereinafter abbreviated as FPDs) made of semiconductor materials have come into practical use as image capturing apparatuses used in medical image diagnosis and non-destructive tests using X rays. Such radiation imaging apparatuses are used as digital imaging apparatuses for capturing of still image, such as photography, and recording of movies, such as fluoroscopy, for example, in the medical image diagnosis.
Techniques to initialize conversion elements included in the pixels in the FPDs by using switch elements different from switch elements for outputting signals are discussed in such a radiation imaging apparatus, as disclosed in U.S. Patent Application Publication No. 2010/0046711.
In the technique disclosed in U.S. Patent Application Publication No. 2010/0046711, a voltage variation component caused by the rising of a drive signal requires a time depending on the resistance of a drive line and the capacitance of a crossing section before the voltage variation component converges into a certain voltage. In addition, when a transistor having a control terminal (gate) and two main terminals (source and drain) is used as an output switch element, the voltage variation component also requires a time depending on the resistance of the drive line and the capacitance between the gate and the source (Cgs) before the voltage variation component converges into the certain voltage. Accordingly, it is necessary to wait a certain time for the voltage variation component that converges into the certain voltage after an output operation is terminated before a sample-and-hold operation is performed. Since the certain time occurs in units of rows, it is necessary to wait the certain time 1,000 times in order to acquire an image signal corresponding to one image from, for example, a conversion unit of 1,000 rows by 1,000 columns. However, in a case in which it is necessary to shorten the time before the image signal is output, such as in the recording of movies (fluoroscopy), a frame rate that is required may not be achieved if the sample-and-hold operation is not performed within the time when the voltage variation component converges. Since the sample-and-hold operation is performed within the time when the voltage variation component converges in the above case, an electrical signal that is output and held is affected by the voltage variation to increase the amount of a noise component, thereby decreasing a signal-to-noise ratio (S/N ratio) of the image signal captured by the imaging apparatus. Consequently, it is difficult to reduce the time (frame time) necessary to read out the image signal, for example, during which the recording of movies at a frame rate of 30 frames per second is achieved, without decreasing the S/N ratio.